This invention relates to the field of person-machine interfaces; specifically, it relates to the field of tracking-pointer devices. The present invention improves tracking a light pointer on any type of display.
The prior-art tracking device used with large-scale or group displays employs a computer that analyzes the display and determines the location of a user-operated pointer that interacts with the display. The pointer is typically a battery-operated light or laser pen that illuminates an element of the display. A video camera trained on the display transmits its image to a computer. The computer analyzes the image frame by frame to determine the current position of the pointer on the display.
This prior-art device uses software and a video capture card in a PC to analyze the video. The video capture card creates a bitmap of the display that the software searches for the brightest isolated spot. Once the software finds this spot, it records its coordinates, which correspond to the location of the spot. The video capture card accepts data from a video camera one frame at a time. In the prior-art device, the PC must process the entire captured video bitmap using software. As such, the rate at which the prior-art device can operate equals the sum of the time required to capture the video, the time for the software to run through its sequence, and the time associated with the inherent processing speed of the PC. As an example, a prior-art device based on a 200 MHz Pentium PC will produce pointer coordinates from the corresponding video frame bitmaps at a rate of 15 per second. A computer system can use the coordinates provided by the prior-art-tracking device in a number of ways; the most common is to treat the pointer like a mouse.
This prior-art device suffers several limitations. It cannot operate in real time, as searching for the bright spot cannot begin until the capture card has loaded an entire frame of video. The built-in delay is therefore never less than the time required to completely search a given frame. The prior-art device is also limited in both resolution and update rate, which depend on the processing power available. A minimally acceptable 240xc3x97320-pixel image at 15 frames/second fully consumes the resources of the example 200 MHz Pentium PC. Lastly, even a minimal system of the prior art can cost several thousand dollars.
Thus there is a need for a system that tracks the pointer of any two- or three-dimensional display in real time with high resolution, rapid update, and at lower cost than the devices presently available.
An object of this invention is to track a pointer on a display in real time.
Another object of the present invention is to operate in both two- and three-dimensional space.
Still another object of the present invention is to track a pointer on a display with a camera resolution greater than 240xc3x97320 pixels and at a rate faster than 15 frames per second.
Yet another object of this invention is to track a pointer across a single display or across multiple displays.
The present invention performs these tasks at a great reduction in cost from prior-art devices. The present invention addresses the limitations of the prior art by eliminating the computer from the system, replacing it with custom hardware that functions in substantially real time in both two- and three-dimensional space with readily expandable resolution. Construction costs are a fraction of those for a prior-art computer-based device.
The present invention improves tracking a user-operated light pointer on any type of display by combining a microcontroller, video processing logic, a pair of counters and a latch, and real-time control logic that together track the pointer image. A camera on the display sends video data to the device of the present invention, which looks for the point of greatest intensity in the video. This point corresponds to the location of the pointer. Two counters and a latch store the current location of the pointer""s image on the display. One counter holds the pixel location, the other counter holds the line location, and the latch holds the value of the field, odd or even. Timing information, input along with the video, controls the counters and latch. Changing the resolution of the device requires extending each counter in bits and making the clock run faster. When the pointer is located in the video, the counters and latch are stopped and their values provided to the system in substantially real time via the microcontroller.
A comparison between the present invention and a prior-art device based on a 200 MHz Pentium PC demonstrated the several advantages of the present invention:
First, speed: The present invention easily detects the pointer each time the video scans the pointer. The prior-art device can maintain consistently a detection rate of only 20-25% of the scan.
Second, timeliness: The present invention begins to report detection almost immediately after the video processor xe2x80x9cseesxe2x80x9d the pointer. The prior-art device must always complete a fall frame before it can begin its search for the pointer.
Third, resolution: To sustain a 10-15 Hz update rate, the prior-art device is limited to a resolution of 240xc3x97320 pixels. The present invention currently operates at 480xc3x97512 pixels. Its resolution can be increased without penalty to any practical value. Only the type of camera limits the maximum resolution.
Fourth, technical obsolescence: The prior-art device is limited to use with analog-only cameras as a result of its dependency on the video capture card. The present invention is not so limited; it can capitalize on the recent proliferation of compact digital video cameras that have analog outputs, digital outputs, or both.
Fifth, cost: The present invention costs less than $150. The prior-art device costs in excess of $2,500.
Briefly stated, the present invention provides apparatus and method to track a light pointer on a display. The device processes analog interlaced field video images from a video camera, seeking the point of brightest intensity, which is the current location of the pointer on the display. Synchronously operating counters and a latch count the lines and pixels of the video data until a high-speed comparator detects the brightest point of the video data. The comparator then sends a detect signal, causing control logic to freeze the counters, as well as freezing the latch, effectively storing in the counters and latch the line and pixel location of the pointer. The same detect signal from the comparator instructs a microcontroller to output the data from the counters in various digital data formats, one such being RS 232. The device operates in substantially real time in either two or three-dimensional space, with greater speed and significantly reduced cost over the prior art, and an adjustable resolution.
According to an embodiment of the invention, an electronic tracking device whose output is absolute x and y coordinates of a light pointer""s image on a display and synchronization information, comprises: a microcontroller; video-processing logic; two synchronized counters; a latch; and control logic.
According to a feature of the invention, a method of tracking a user-operated light pointer on a passive or active single display, or passive or active multiple displays, comprises the steps of: simultaneously inputting frames of video to a tracking device, the frames of video comprising interleaved fields; detecting the light pointer""s image on the display; counting lines and pixels in the frames of video until the pointer""s image is detected; determining and storing a value of a current one of the interleaved fields, the value being odd or even, until the pointer""s image is detected; stopping counting the lines and the pixels when the pointer""s image is detected; producing a position of the pointer""s image, the position comprising absolute x and y coordinates of the position and a synchronization bit; and resetting the step of counting to minimum values after the step of producing.
According to another feature of the invention, apparatus for tracking a user-operated light pointer on a passive or active single display, or passive or active multiple displays, comprises: means for simultaneously inputting frames of video to a tracking device, the frames of video comprising interleaved fields; means for detecting the light pointer""s image on the display; means for counting lines and pixels in the frames of video until the pointer""s image is detected; means for determining and storing a value of a current one of the interleaved fields, the value being odd or even, until the pointer""s image is detected; means for stopping counting the lines and the pixels when the pointer""s image is detected; means for producing a position of the pointer""s image, the position comprising absolute x and y coordinates of the position and a synchronization bit; and means for resetting the means for counting to minimum values after the means for producing has produced the position.
The above and other objects, features, and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.